1. Field of the Invention
The present invention relates to an improved technique for the construction of sensors by making use of the properties of a pressure-sensitive and conductive elastomer, and more particularly to a technique of largely improving the construction of a pressure-sensitive portion to sense a pressure and thereby having the construction possess the function as a tactile means which has not so far existed, being further concerned with sensors having particular utility in devices and equipment provided with a tactile means such as pressure-sensitive sensors, for example, industrial robots operated in the fields of food handling, medical treatment, and the like.
2. Description of the Related Art
Among materials which, when not under pressure, display a high value of electrical resistance and come to possess insulation properties, and when put under pressure, display a low value of electrical resistance by being compressed and deformed and come to possess conductive properties, there are known in the prior art pressure-sensitive and conductive elastomers typically represented by pressure-sensitive and conductive rubber, which are disclosed in, for example, Japanese Examined Patent Application Nos. SHO-(56)-9187, SHO-(56)-54019, SHO-(60)-722, SHO-(60)-723 and the like.
This type of pressure-sensitive and conductive elastomer is composed by mixing and dispersing conductive particles, such as metals and granulated carbon, with insulating substances made of rubber or elastomer, having the material that it becomes an insulating properties when it is not under pressure because conductive particles are spaced from each other, and, when placed under pressure, it displays a decreasing value of electrical resistance and becomes a conductive substance because conductive particles are made to approach or contact each other.
There are known in the prior art the application of such properties of pressure-sensitive and conductive elastomer, in which, as illustrated in FIG. 21, flexible print substrates 101, 102 which are in the film state are arranged on the upper and lower surfaces of a pressure-sensitive and conductive elastomer 100, respectively. And groups of electrodes 101a . . . 101a and other groups of electrodes 102a . . . 102a are arranged in many lines and at the predetermined intervals on the print substrates 101, 102, respectively, are made to cross at right angles with respect to each other. In this sensor, when the pressure-sensitive and conductive elastomer 100 is compressed and deformed by a pressure given on a particular spot, a continuity condition is established between the electrodes 101a of the print substrate at the upper side and the electrodes 102a of the print substrate 102 at the lower side, the locations of which correspond to the above-mentioned particular spot. It is then possible to assign the X-Y coordinates at a spot to which a pressure is given from positions in the X direction of the electrodes 101a and in the Y direction of the electrodes 102a, which are both in the continuity condition. Furthermore, the quantity of the pressure is known by the quantity energized at the establishment of the continuity condition.
There have been, however, disadvantages in the afore-mentioned conventional sensor.
Because the flexible print substrate 101 arranged on the upper side of the pressure-sensitive and conductive elastomer sheet 100 is composed by sticking the electrodes made of copper or aluminum foil onto the film made of plastic materials such as polyester or polyamide, the pressure force which is given from above does not act directly on the pressure-sensitive and conductive elastomer sheet 100 but acts thereon indirectly or through the flexible print substrate 101. The pressure force is then dispersed by the flexible print substrate 101, and, consequently, the resolving power is decreased to the degree less than that to be exerted by the properties of the pressure-sensitive and conductive elastomer sheet 100.
Furthermore, the above-mentioned sensor can detect the only and one direction in which a pressure acts, which is the direction perpendicular to the upper surface of the pressure-sensitive and conductive elastomer sheet 100. A pressure oriented in the direction parallel with said upper surface is not detected. Objects detectable are limited to a position of X-Y coordinates which is under pressure and the quantity of the pressure. If a pressure is obliquely given, it is impossible to discriminate the left, right, forward or backward direction wherein a pressure is given. The above-mentioned conventional sensor is, therefore, not useful as a direction sensing means.
The present invention is made in view of the above-mentioned disadvantages and directly addressing the problems of a decrease in resolving power and the inability of detecting the direction of pressure. The present invention provides with high resolving power and the capabilities of detecting a number of directions wherein pressures are given, of discriminating the oblique, left, right, forward, and backward directions, and of efficiently functioning as a tactile means.